Parent two objects, without the child getting moved by the parent
This can be done fairly quickly; what you need to do is and an empty to the location of the child, and then make the child copy the location of the empty, using a constraint &mdash; now you can safely parent both objects and the child won't move. 

You can do this by:


While in Edit mode, and with the child selected, pressing Shift + S > Cursor to selected
Pressing Shift + A > Empty > Plain Axis
Selecting the child, going to the Constraints tab of the Properties window and adding a  Copy Location constraint, with the target set to the empty created earlier